Journal
UNIVERSE
Volume 8, Issue 11, Pages -Publisher
MDPI
DOI: 10.3390/universe8110552
Keywords
cosmological neutrinos; neutrino physics; physics of the early universe
Funding
- IBS [IBS-R018-D1]
- JSPS [JP18K18764, JP21H01080, JP21H00069]
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This paper reviews the distortions of relic neutrinos due to interactions in the early universe and their implications on the Cosmic Neutrino Background in the current universe. It also highlights the importance of experimental studies related to these effects.
We review the distortions of spectra of relic neutrinos due to the interactions with electrons, positrons, and neutrinos in the early universe. We solve integro-differential kinetic equations for the neutrino density matrix, including vacuum three-flavor neutrino oscillations, oscillations in electron and positron background, a collision term and finite temperature corrections to electron mass and electromagnetic plasma up to the next-to-leading order O(e(3)) . After that, we estimate the effects of the spectral distortions in neutrino decoupling on the number density and energy density of the Cosmic Neutrino Background (CvB) in the current universe, and discuss the implications of these effects on the capture rates in direct detection of the CvB on tritium, with emphasis on the PTOLEMY-type experiment. In addition, we find a precise value of the effective number of neutrinos, N-eff = 3.044. However, QED corrections to weak interaction rates at order O(e(2)G(F)(2)) and forward scattering of neutrinos via their self-interactions have not been precisely taken into account in the whole literature so far. Recent studies suggest that these neglections might induce uncertainties of +/-(10(-3)-10(-4)) in N-eff.
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